Foamed hollow continuously cast articles are more particularly used as foamed material insulating tubes, that is to say more especially for thermal insulation on heating or cooling pipes. For the continuous production of foamed material insulating articles a method has been previously proposed in the case of which on to a rotating core body which is furthermore moved longitudinally, a basic material adapted to foam is applied, which can foam outwards freely, since on the outside no delimiting means are provided. This results in the disadvantage that insulating tubes of foamed material produced in this manner have an irregular outer surface and furthermore on fitting to a heating pipe must be encased in an additional covering foil. There is also the further disadvantage that the wall thickness of the foamed material tube is uneven.
Furthermore a device has been proposed comprising a stationary outer mold tube with a slot at the top, whose longitudinal slot serves for the introduction via a flat connecting piece of a cylindrical rod concentrically in such a manner that an annular channel is produced which at the top is interrupted by the connecting piece. On both sides adjacent to the connecting pieces the edges of inner and outer foils, necessary for tube production, are drawn from the outer mold tube upwards, where they are pressed by two conveying chains against the connecting piece and are moved in the longitudinal direction. Before the entry of the two foils into the molding channel the outer foil, which has previously been buckled outwards, is coated with a foam material mixture. On passage through the annular mold channel the foam material mixture foams and while pressing the outer foil against the inner wall of the outer mold tube and pressing the inner foil against the cylindrical core is forced through the annular molding channel. After emerging from the mold channel the excess foil edge portions which project to the outside are cut off and the tubular extruded article which is thus produced is cut up into suitable lengths. A disadvantage in the case of this method of production is more especially the considerable friction between the outer foil and the outer mold, since this limits both the length of the apparatus and therefore the speed of production and also the use of the materials coming into question, this being because high quality foaming materials produce higher reaction pressures on foaming. These reaction pressures are however limited as regards their upper limits, because an increase in the reaction forces simultaneously brings about a very pronounced increase in friction. A further disadvantage is due to the fact that there is only a restricted choice as regards the construction of the core . Another disadvantage is due to the fact that not only an outer foil but also an inner foil must be employed, which furthermore on the side adjacent to the core must be provided with a lubricant in order to keep friction within limits. This inner foil is only to aid manufacture, it is not required for later use of the foamed material tube as an insulating tube. Furthermore the inner foil leads to an unnecessary complication of the manufacturing process and therefore increases (the liability to breakdown of the installation.
Furthermore the German Pat. Specification (Auslegeschrift) No. 1,266,485 describes a continuous method in the case of which for the production of a longitudinally slotted foamed material insulating tube it is also necessary to employ an inner and outer foil. The two foils are so introduced to an annular molding chamber while being caused to bend in a tubular manner outwards that the outer foil comes to lie against the outer wall and the inner foil comes to lie against the inner wall formed by the core and shortly before entry of the foils into the molding chamber reactive material adapted to foam is introduced into the outer foil and it then immediately foams in the molding channel and becomes joined to the two foils. The molding channel is in this case formed by two circulating outer mold chains and the stationary core, which is attached to a cross-piece, which extends out of the space between the two outer mold chains through an upper joint or gap in an upward direction. In the case of this known method as well there are on the one hand the disadvantages already mentioned above, which are due to the use of an additional inner foil. Furthermore however there is more especially the disadvantage also that very pronounced frictional forces occur at the outer wall of the stationarily arranged core so that in the case of this known method as well the field of applicability is limited with respect to the speed of working, the cross-section of the parts to be produced and the choice of materials adapted to foam which can be employed.
The same also applies as regards another previously proposed apparatus, which has a stationary mandrel as an inner core, which is fixed at the inlet of the installation and extends freely into the stationary or circulating outer mold. Furthermore in the case of this installation it is also necessary to employ an inner foil, and in this case as well difficulties arise to a considerable extent as regards the friction produced. Such difficulties cannot be overcome by the use of additional lubricants. Furthermore there is the added disadvantage that the mandrel, which is only held at one end, is not sufficiently firmly positioned in order to resist the pressures occurring on foaming, without deflection.
Owing to the problem of the above mentioned deflection of the mandrel the proposal has been made in the case of another prior art installation (German Pat. Specification (Auslegeschrift) No. 2,165,584) of using a laser ray to check the deflection and using regulating and controlling elements to ensure proper alignment. By means of this auxiliary device it is however not possible to ensure any satisfactory alignment of the stationary inner core while on the other hand the whole installation becomes relatively complicated.
Furthermore a method and an apparatus have been proposed which depart from the method in accordance with the German Pat. Specification No. 1,266,485 in that it is not only the two outer mold chains but also the core which circulate, that is to say the core is not arranged in a stationary manner and instead is displaced pari passu with the two co-axial outer mold chains. This leads to the advantages of a substantial reduction of friction and a substantial increase in the speed of operation. However a further simplification of the method and of the apparatus would be desirable, together with provision for the possibility of production of multi-layer hollow continuously cast articles together with the possibility of providing the hollow cast article with various geometrical forms internally or externally as for example grooving. There is furthermore the disadvantages with all previously proposed methods and apparatus that the hollow cast articles must be subsequently separated into two half-shells, since half-shells are required for the simplest possible fitting on the pipes which are eventually to be insulated. Added to this in the prior art there has always been the disadvantage of undesired transfer of heat along the joint. There is also the disadvantage with previously produced insulating tubes that despite complete separation into the two half-shells they must be transported in the folded together condition since the half-shells are connected at least by a foil. The consequence of this is a larger requirement on storage and for transport.
The last mentioned disadvantage of a greater space requirement in the case of storage and transport is admittedly avoided in the case of another previously proposed method (French Pat. Specification No. 1,573,743) in the case of which the semi-cylindrical shells can be produced from polyurethane foam material by means of two conveyor belts arranged one above the other continuously, which have respective mold halves which lie against each other or fit into each other and so form a closed mold channel which can be displaced along a straight path and whose cross-section is semi-cylindrical. If the cross-section of the cast foam material article to be produced is complicated in shape, for example owing to the presence of undercuts, it is possible to provide a third conveyor belt in order to facilitate detachment of the conveyor belts from the cast foam article.
Although in the case of the above mentioned method friction can be kept relatively low there is however more especially the disadvantage that there is no possibility of producing hollow cast articles with a practically closed annular cross-section, for the cast articles have a semi-cylindrical or possibly rectangular cross-section. Furthermore fitting together of two semi-cylindrical shells to form one hollow cast article with a closed annular cross-section is neither intended (the aim of the invention is the production of cast articles with various solid cross-sections and not production of hollow cast articles) nor promising of success, since in this case it would firstly be necessary to produce in two working operations two semi-cylindrical shells and then the latter would have to joined together in a further working step. In this respect it would firstly not be possible to see how such a joint could be made in order to make possible later use as an insulating tube in the case of which the foam material tube must be opened up or unfolded to a certain degree for fitting but however after fitting is held together resiliently. In the case of a specific embodiment of this known method using a core string with spacers a continuously cast article is made, whose cross-section corresponds to three quarters of a circle. Apart from the fact that to this extent it is not possible to produce a hollow continuously cast article with an annular cross-section which is substantially closed, there is the shortcoming that the core string can only be removed again with comparative difficulty from the cast foamed polyurethane article after it has been produced, for this purpose the spacers must be separated from the core string. A further disadvantage resides in that the spacers cannot be removed from the cast foamed polyurethane article and remain in it. This furthermore has the disadvantageous consequence that at the inlet of the apparatus the core string must be constantly supplied with new spacers. Furthermore on the basis of the use of a core string which by its very nature is relatively thin and flexible it is not possible to produce a cavity with large radius. Furthermore the shaping of the cavity is very imprecise owing to the flexibility of the core string and the incomplete support by the spacers.